Electrophotographic recording methods, sublimation transfer recording methods, thermal transfer recording methods, and inkjet recording methods are exemplified as methods for forming images on recording media such as paper. Among these recording methods, inkjet recording methods have advantages over other recording methods such that efficiency of consumption of the image recording material (i.e., ink) is high (i.e., the method is superior in resource saving); and the cost of the image recording material used for forming an image with a unit area is low. However, inkjet recording methods using an aqueous ink have various problems to be solved. Inkjet recording methods using an ink including an organic solvent have been proposed in attempting to solve the problems, but such organic solvent inks have other problems to be solved.
In recent years, inkjet recording methods using an active energy ray curable ink attract attention. For example, ultraviolet curable inks, which are representative examples of the active energy ray curable ink, have been described in various documents, and typically include a monomer and a polymerization initiator as essential components while optionally including other components such as pigments, oligomers, polymers, and sensitizers as described in OPTICAL APPLICATION TECHNOLOGY AND MATERIAL DICTIONARY published in Japan in 2006 by Industrial Technology Service Center and OPTIMIZATION OF UV CURING RESIN published in Japan in 2008 by TECHNICAL INFORMATION INSTITUTE CO., LTD. Specific examples of the UV curable ink described in OPTICAL APPLICATION TECHNOLOGY AND MATERIAL DICTIONARY include inks including a radically polymerizable compounds such as acrylate compounds (e.g., ethylene oxide adduct of trimethylolpropane triacrylate, trimethylolpropane triacrylate, 1,9-nonanediol diacrylate, isobonyl acrylate, and compounds (oligomers) having the below-mentioned formulae), N-vinyl formamide, and triallylisocyanurate, and inks including a cationically polymerizable compound such as bis(3-ethyl-3-oxetanylmethyl)ether, and CELLOXIDE 2021 (difunctional alicyclic epoxy compound) from DAICEL CORP.

The monomer component in such active energy ray curable inks typically includes plural monomers to optimize the curing speed (i.e., sensitivity), the ink viscosity, and the properties of a film formed by curing the ink. Specifically, a combination of a monomer, which has a low molecular weight and a low viscosity and which has good reactivity, and a monomer which is multifunctional and which has a high molecular weight is typically used. Since the content of the monomer component in such an active energy ray curable ink is about 80% by weight (i.e., since monomers are main components of such an ink), not only development of new monomers but also development of compounding techniques has been actively performed.
For example, JP-2007-231231-A discloses an ink including an ester or amide compound of (meth)acrylic acid which is tri- or more-functional compound having an alkylene oxide group therein. JP-2007-231233-A discloses an ink including a combination of an ester or amide compound of (meth)acrylic acid which is a tri- or more-functional compound having an alkylene oxide group therein, and an ester or amide compound of (meth)acrylic acid which is a mono-functional compound having an alkyl group having 6 to 12 carbon atoms. JP-2007-67926-A discloses an ink including an aliphatic (meth)acrylate compound having a secondary hydroxyl group, and a compound having a nitrogen atom and a polymerizable unsaturated bond therein. JP-2007-144057-A discloses an ink including a polymerizable compound having an amino group and a polymerizable unsaturated bond therein.
In addition, there are proposals for inks using a monomer compound having a urethane structure. For example, JP-2006-257155-A and JP2009-249561-A have disclosed inks including a urethane acrylate oligomer. JP-2010-181677-A discloses an ink including a low molecular weight (meth)acrylate monomer having a urethane structure. In attempting to enhance the curability of ink, and the flexibility of the cured film of ink, JP-2007-138118-A discloses an ink including a monomer having an aliphatic ring structure, and JP-2007-177174-A discloses an ink including a monomer having a heterocyclic structure such as dioxolan or dioxane. In attempting to reduce the viscosity of ink while enhancing the curability of ink, and the solvent resistance and adhesiveness of the cured film of ink, JP-2009-179681-A discloses an ink including two or more of monomers which have an aliphatic ring structure, a heterocyclic structure or an aromatic ring structure.
In addition, there are proposals for inks including a monomer having two different polymerizable functional groups therein. For example, inks and a diluent, which use a compound having both a (meth)acrylic acid ester group and a vinyl ether group have been disclosed in JP-3461501-B1, JP-3544658-B1 (i.e., WO2003/089486), JP-2012-140551-A and JP-2012-140583-A.
When the above-mentioned inks including a polymerizable compound (monomer) are used, odor is a major problem to be solved. In general, active energy ray curable inks include a large mount of diluent, which is typically a low molecular weight reactive monomer and which serves as a solvent of the inks, to properly control the viscosity of the inks. However, such low molecular weight monomer compounds typically have an unpleasant odor.
For these reasons, the inventors recognized that there is a need for an ink which has a good combination of reactivity (photo-polymerizability) and curability (hardenability) and which hardly smells.